This invention concerns a leg prosthesis for adaptation to a thigh stump. It is composed of an adapter for a knee joint, as is known from U.S. Pat. No. 3,947,897, for example. It is anchored with a post part in the stump of the femur. The adapter comes out of the thigh stump on the distal side, and there it can be coupled to an artificial knee joint, as is known from EP-B-0 358 056, for example.
A prosthetic lower leg is usually coupled to the knee joint, and it in turn has a prosthetic foot attached on the distal side. The foot can be swiveled into the heel position.
In the proposal in EP-B-0 358 056, for example, the knee joint is designed so that it makes a combined rolling and sliding motion on a swivel axis when it goes from the extended position into the bent position. Unlike a purely hinged joint, the knee joint of the generic leg prosthesis is designed so that the distance from a point on the knee joint in front of the swivel axis, seen dorsally, to the end of the prosthetic lower leg steadily decreases. In other words, the distance from a point in front of the swivel axis, seen ventrally, on the other hand, to the end of the prosthetic lower leg steadily increases.
One problem for patients with partially amputated upper legs is, inter alia, that they have to walk with the healthy foot in a tip-of-the-foot position when they walk to allow the prosthetic foot to oscillate with the leg prosthesis when they take another step. This is true regardless of whether the prosthetic foot can now swivel on the prosthetic lower leg or is stopped tight to it. The need to put the healthy natural foot into a sharp or extreme tip-of-the-foot position, so that the prosthesis can oscillate, requires a very non-physiologic way of moving and thus puts a lot of stress on the spinal column when walking along.
On this background, the problem of this invention is to create an aide here, i.e., to further develop a generic leg prosthesis so there is no longer any need to put the healthy natural foot in a non-physiologic tip-of-the-foot position to allow the artificial leg to oscillate and so the motion seems more natural.
This problem is solved by placing a force-transmitting element between at least one mounting point in front of the swivel axis, seen from the dorsal side, and/or a mounting point in front of the swivel axis, seen from the ventral side, and the prosthetic foot, so the force-transmitting element moves the prosthetic foot when the knee joint is bent from the tip or mid-foot position of the artificial foot more into a heel position.
The knee movement thus actively controls a positioning force introduced into the prosthetic foot, in such a way that the more the knee bends, the more the prosthetic foot is put into the heel position. This shortens the stroke necessary for the healthy foot, and the leg prosthesis can oscillate slightly 5 to 10 mm in a way that allows the patient""s motion to appear more natural.
The condition that the distance from a point in front of the swivel axis, seen from the dorsal side, to the end of the prosthetic lower leg steadily decreases is crucial. In a knee joint with a pure hinge joint, this condition would not exist, for example, The then given polar curve would also bring with it a displacement of the distance, for example, with the first movement from the extended position to the bent position. But after it reached a dead point, the distance would increase again. In a leg prosthesis, when the complete movement of the knee joint is executed from the extended position to the bent position, this would make the foot first swivel slightly into the heel position, after it exceeded the dead point mentioned, but it would be swiveled back into the starting or tip-of-the-foot position, so as a result when the knee joint is fully bent, there would again be a quasi-tip-of-the-foot position of the foot in relation to the prosthetic lower leg. But this is precisely the phenomenon to be avoided, so then there is no more need to bring the healthy foot more sharply into the tip-of-the-foot position so the leg prosthesis can oscillate.
One preferred embodiment provides that the force-transmission element be designed from a push rod jointed on the knee joint and on the prosthetic foot. On the proximal ends, the push rod can be jointed in the dorsal area of the knee joint, for example, in order to move the prosthetic foot from the starting position into the desired heel position while reducing the distance from the joint to the end of the prosthetic lower leg for the swivel movement.
The prosthetic foot is moved very reliably into the heel position when the knee joint moves from the extended position into the bent position, if the leg prosthesis is designed, as in one advantageous variation, so that the prosthetic foot is coupled to the prosthetic lower leg so it can swivel around a swivel point placed ventrally, and the force-transmission element is jointed on the prosthetic foot on a mounting point placed dorsally. The force-transmission element then causes torque around a mounting point placed dorsally, and the prosthetic foot swivels safely into the heel position.
Another preferred embodiment provides for flexible adjustable reins to be stretched to their effective length between the prosthetic foot and a bearing on the prosthetic lower leg, and the slack increases as the bending of the knee joint increases.
The reins basically do the work of the natural Achilles heel. The main job of the reins is to bring the foot back into its starting position when the knee joint is in the extended position. Because of the possibility of setting their effective length, for example with a threaded stop to which the end of the reins in question can be screwed, the reins are also used for individual adjustment of the tip-of-the-foot setting of the prosthetic foot. This adjustment generally differs with different heels from patient to patient.
A reset element is preferably built into the force-transmission element, and when the knee is extended, after being bent, it actively brings the prosthetic foot back into its starting position. This active reset element supports the effect of the reins mentioned above in the beginning movement from the bending position into the extended position of the knee. First, the force-transmission element mentioned triggers the reset effect, and the effect is triggered when the reins reach their extended position.
With the above-mentioned variation, it is preferred that the reset element have a guide case holding a spiral spring and a piston that goes into the case as part of the push rod, in such a way that, as the bending of the knee joint increases, the spring is put under increasing pressure and when the knee joint is extended, the spring force swivels the prosthetic foot into the starting position. The harder the knee is bent, the higher the spring forces that will be produced in the reset element.
Finally, it is advantageously provided that the guide case be mounted in a housing attached to the prosthetic lower leg. This produces a relatively standard compact unit for the patient to handle.